Developing device for electrophotography



June 24, 1969 KAZUQ OBUCH| ET AL 3,451,376

DEVELOPING DEVICE FOR ELEC'IROPHOTOGRAPHY Filed Nov. 8, 1967 KAZUO OBUCHI HARUNOBU KATO ATTORNEYS.

United States Patent US. Cl. 118637 3 Claims ABSTRACT OF THE DISCLOSURE The developing device for electrophotography in the form of an enclosure having side and top walls and conveyer means for moving a base plate longitudinally through the enclosure, the base plate carrying a layer of photoconductive powder bearing an electrophotograph1c latent image, an inclined baffie and guide plate pivotably coupled to the entry end of the enclosure with the free end of the inclined bafile and guide plate normally resting on the conveyer means but contacting the powder covered surface of the base plate and inclined in the direction of base plate movement, means at the exit end of the enclosure for directing an air current onto the powder carrying surface of the plate and suction means carried by the enclosure at the entry end above the pivoted baflle plate for sucking powder particles blown upwardly along the inclined bafile and-guide plate and removlng the same.

In the field or electrophotography in which a photoconductive powder, as described in detail in Japanese Patent Publication No. 22,645/ 1963, the practice is now to produce a uniform layer of charged photoconductive powder on a base plate and then after exposing this layer to light by projecting an image thereon, the image 15 formed by the powder on the base plate by selectively removing therefrom the powder particles which have lost their respective electrical charges, the attractive forces to the plate being proportional to the quantities of light the particles have received. In this connection, it has been a practice to use air current as the means for removing the powder whose attractive forces weaken to thereby obtaln the visible image. It is conventional in developing to use an air current which is driven nearly perpendicular to the surface of the moving base plate. When this method is applied, most of the removed powder is scattered over the undeveloped portion of the base plate, and conse quently, the undeveloped portion of the plate accumulates the powder as it moves. For this reason, it has been impossible, especially in the case where a long base plate is used, to make stable images due to the apparent inability to remove the scattered powder particles by air current and therefore, this leads to the destruction of the electrostatic latent images.

It is, therefore, an object of this invention to provide a developing device which employs air current to remove the powder particles which have lost their charge, and in which it is possible to achieve stable developing of a long base plate by preventing the removed powder particles from scattering over the undeveloped portion of the base plate.

Other objects of this invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side view, in section, of a preferred embodiment of the developing device of this invention in which the electrophotographic base plate is about to move into the developing device enclosure.

FIGURE 2 is a side view, in section, of the apparatus of FIGURE 1 with the electrophotographic base plate positioned within the enclosure.

FIGURE 3 is a side view, in section, of the apparatus of FIGURE 1 with the electrophotographic base plate moving out of the exit end of the device enclosure.

FIGURE 4 is a side elevational view, in section, of an alternate form of the present invention.

FIGURE 5 is a side elevational view, in section, of yet a third embodiment of the present invention.

Referring to FIGURE 1, the developing device, indicated generally at 10, comprises an enclosure having spaced side walls 12 and a top wall 14 with the enclosure being completed by moving conveyer means 7. There is thus formed a rear exit end 16 of the enclosure which is open, and an entry end of the enclosure 18. At the entry end 18 of the enclosure, there is provided a baffling and guide plate 2 which is pivotally mounted at 3 for free swinging, the pivoting means 3 comprising hinges or like means. The baflle and guide plate 2 normally has its free edge in contact with the upper surface of the conveying means 7, the bafiie and guide plate 2 being inclined in the direction of movement of the conveyer means 7, as indicated by the arrow. Wall members 4 act in conjunction with top wall 14 and side wall 12 to prevent the air current and the powder particles removed from the electrophotographic base plate from being scattered about the wall elements 4 acting to form a duct and connected to a suction device (not shown). An electrophotographic base plate 5 which is electrically conductive, or whose surface is treated as to be electrically conductive, carries a photoconductive powder layer 6 which retains an electrostatic latent image and which moves into the developing device enclosure on the conveyer means 7, as indicated by the arrow. When the electrophotographic base plate 5 passes under the pivotable bafile and guide plate 2, the baffie and guide plate 2 swings upwardly about its pivotable support means 3, as best shown in FIGURE 2, without obstructing the advance of the base plate 5. A blower 20 is provided with an air outlet 1 for directing pressurized air onto the powder covered surface of the electrophotographic base plate 5, as the plate enters the enclosure and moves toward the exit end 16. Of the photoconductive powder particles carried by the base plate 5, only those whose attractive force has been lessened because of exposure to light are blown away. As the powder 8 is scattered by the air current issuing from the outlet 1, it is intercepted by the bafile and guide plate 2 and thus, the blown powder particles are not scattered over the undeveloped portion of the base plate, which as indicated in FIGURE 2 is at that point exterior of the enclosure and lying underneath the inclined battle and guide plate 2. Instead, they go upwardly along the inner surface of the guide plate 2 and are sucked into the duct area formed by the walls 4 and into a powder recovering system (not shown) by virtue of the suction force developed within the duct area formed by members 4. In this way, an image 9 of powder is formed upon the base plate as the base plate 5 leaves the development area. After the electrophotographic base plate 5 moves out from under the baflle and guide plate 2, the bafile and guide plate fall asa result of gravity onto the surface of the conveying mechanism 7 which may constitute a truck or belt. As indicated in FIGURES 2 and 3, the powder 8 is removed from the base plate and is sucked into the recovering system (not shown), as indicated by the inclined arrows, the base plate is then developed.

In the practice of this invention, it might be feared that, owing to the fact that the baffle and guide plate 2 come into contact with the photoconductive powder layer 6 on the base plate 5, the baffie and guide plate might disturb this layer and unfavorably affect the development of the latent image. However, since the photoconductive powder layer 6 is comparatively thin, and is firmly attached to the base plate 5 in the image portion, the effect of the contact by the baffle and guide plate 2 'will not be adverse, unless an exceedingly heavy baffle and guide plate is used. As a result of experiments, such common materials as aluminum, iron, copper, polyvinyl chloride or baflle and guide plates formed of veneers of the same, in order of 0.5 mm. to 2 mm. in thickness operate satisfactorily. In order to obtain increasingly satisfactory development of images, flexible material may be provided along the edge of the baflle and guide plate in order to obtain closer contact between the baffle and guide plate and the powder carrying base plate 5. Also, a substance of low friction coefficient may be provided along the edge of the baffle and guide plate 2. In regard to the angle of inclination of the baflle and guide plate 2, the angle should range horizontal and 45 to the base plate 5. As the angle becomes near to vertical (90), it is more difficult for the removed powder particles to be satisfactorily recovered. Further, it is necessary that the edge of the guide plate 2, whether it is being carried by the base plate or the surface of the conveying mechanism, must contact the same to function effectively. For this reason, it is necessary that the bafffe and guide plate 2 have an adequate length so that the angle of the plate may not vary considerably due to the difference in elevation between the surface of the conveyer 7 and the powder surface 6 of the base plate. The longitudinal distance between the edge of the baflle and guide plate 2 and the area of discharge of the air current from blower 20 is predetermined such that the air current will not disturb the subsequent development of the image carrying plate, and further, that the suction force created within the duct formed by members 4 on the powder recovery system may operate effectively. It should be noted that the powder particles of which the attractive force has decreased, are not removed in the area just below the outlet 1 for the blower 20 but begin to be removed under the influence of air current moving through the enclosure and into the duct area formed by members 4 even before the powder particles carried by the base plate 5 reach the area of the outlet 1 of the blower 20. The removal is completed from just under the blower discharge. The guide plate 2, therefore, should be arranged so as to have its edge a certain distance from the vicinity of the air current outlet so that the guide plate edge is sufficiently removed from the area in which most of the powder removal takes place. On the other hand, if the edge of the guide plate is too far from the air current outlet 1, the speed of the powder near the baffle and guide plate 2 is unnecessarily slowed down and for optimum operation would require a recovery system (suction means) of large windability which would be a disadvantage. Taking this into consideration, it is necessary to properly determine the distance between the air current outlet 1 and the edge of the guide plate 2. However, if the difference in elevation is large between the surface of the base plate 5 and the surface of the conveying mechanism 7, and if the development is to be made starting from the leading edge of the plate 5, this leading edge is hardly influenced by the air current until it comes just below the air current outlet 1. Consequently, from the leading end the powder particles will not be removed as efficiently as from other portions of the base plate and the resultant development will be such that the leading end of the image is foggy. It is possible to make uniform the developed condition over the complete surface of the base plate 5 by lessening the distance between the air current outlet 1 and the edge of the guide plate 2 so that other portions of the base plate, as well as the leading end portion has its powder influenced by the air current in the vicinity of the air current outlet. In this case, because the development area is unnaturally limited, there must be an incre ed 110w of air c rren in order to mak the development free from overall fog. Furthermore, there may arise the situation where, because of the wind velocity becoming very high near the edge of the guide plate 2, an air current is created that blows between the guide plate 2 and the base plate 5 causing the powder particles to be scattered over the undeveloped portion of the base plate which has not yet entered the enclosure. In the case of an elongated base plate, such scattered powder particles may disturb the image quality as a result of their accumulation over the plate. In this particular case, two (or more) baflie and guide plates are provided. Reference to FIG- URE 4 shows a second baffle and guide plate 2 pivotably positioned within the enclosure, downstream of the first pivoted baffle and guide plate 2, the free edge of baflle plate 2' also resting on the surface of conveyer mechanism 7 with the other end pivoted by hinge means 3 or the like. Thus, two or more baffle and guide plates may be provided, at suitable intervals, to make the bafiiing effect more perfect.

On the other hand, the contact force applied by the baflle and guide plate 2 to the coated base plate 5 varies according to the dead load of the guide plate 2 and the differential pressure between the interior and exterior surfaces of the baffle and guide plate. The differential Pressure sharply varies depending upon the variation of the rate of air current inside the guide plate 2, and, therefore, if the channel of the air current inside the baffle and guide plate 2 is narrowed by the passage of a fairly thick base plate 5 or the flow rate of air in the powder recovering system is increased according to the properties of the powder to be removed, the inside pressure may become so low that the baflle and guide plate 2 will be lifted up by suction and no longer serve as a baffle and guide plate means, since the edge normally in contact with the base plate 5 is positioned above this plate. A device for preventing this is shown in FIGURE 5 and the device is quite effective to prevent the uplift of the guide plate 2 and to keep the guide plate 2 always in contact with the base plate 5 under a fixed pressure. In FIGURE 5, the upper wall has, at its base plate entry end, duct members 44 coupled to suction means (not shown). A hinge-like member 3 pivotably couples the baflle and guide plate 2 in like manner to the FIGURE 1 embodiment such that the free end contacts the upper surface of moving conveyor means 7. The wall 14 is also connected to the baffle and guide plate 2 by an inflexible bar-like member 11 having rotatable joints 22 on both ends, the upper wall member 14' being pivotably connected to duct wall element 4 by hinge means 3". Therefore, changes according to the variation of the rate of air current cause the forces acting on the guide plate 2 and the upper wall 14' to cancel each other ensuring that the contact force of the plate 2 on the base plate 5 remains constant to ensure stable development of the images carried by the base plate.

If the developing device of this invention is applied in the electrophotographic process using a broad baseplate, a base plate of various shapes and sizes, or an uneven base plate, it is practical to divide the aforementioned guide plates 2 and 2 into proper sections in the direction of their breadth so that each section may operate independently, and this is also advantageous in terms of powder recovery ratio.

By the use of the invention as described above, it is possible not only to perform a very satisfactory development of an electrostatically applied latent image with a high contrast of image because in no case the photoconductive powder removed during the development process is scattered over the developed and undeveloped portions of the base plate and does not accumulate on the base plate to make development impossible or deteriorate the image quality. It is also possible by the use of this invention to recover, at an exceedingly high ratio of recovery, the photoconductive powder removed as a result of development, because the air current flows in one fixed direction only and the powder particles which have left the base plate are led into the recovery system by the unidirectional air current flowing over the base plate. Thus, it is possible to greatly reduce the costs of photographic processing. Furthermore, the mere fact that the air current is unidirectional simplifies greatly and facilitates the adjustment of developing conditions.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electrophotographic developing device comprising an enclosure including spaced side walls and a top wall, conveyor means forming a bottom wall and acting to move a base plate having thereon a layer of photoconductive powder bearing an electrophotographic latent image through said enclosure, means at the enclosure exit end for directing an air current onto said powder carrying surface of said base plate as it moves through said enclosure, a bafile and guide plate carried by said enclosure at the base plate entry end, said bafiie and guide plate being pivotably coupled to said enclosure and inclined in the direction of plate movement with its free edge adapted to contact said powder carrying surface of said base plate as it moves into said enclosure, and duct means carried by said enclosure at said entry end above said pivota'ble baflle and guide plate for removing powder particles blown upward along said inclined baflle and guide plate.

2. The device as claimed in claim 1 further including at least one additional bafile and guide plate carried by said enclosure downstream of said entry end bafile and guide late, inclined in the direction of base plate movement and adapted to contact said base plate with its free edge.

3. The developing device as claimed in claim 1 in which the top wall of said enclosure is pivotably coupled at its entry end with its rear end adjacent said air current directing means being freely movable away from said conveyer means, and an inflexible, bar-like member pivotably connected to said top wall downstream of said pivot point and to said baffle and guide plate in the vicinity of said base plate contacting edge, whereby a constant force is exerted by said bafiie and guide plate on said base plate as it moves longitudinally through said enclosure.

References Cited UNITED STATES PATENTS 890,252 6/ 1908 Thompson 2633 2,279,553 4/1942 Bradt 1l863 XR 3,038,442 6/1962 Jones et al 118309 XR 3,172,780 3/1965 Csok et a1. 118326 XR 3,229,447 1/1966 Kosta 117-1()2 XR 3,239,863 3/1966 Gardner 15345 XR 3,332,328 7/1967 Roth 118637 XR PETER FELDMAN, Primary Examiner.

US. Cl. X.R. 

